Contact lenses have been utilized for many years for the correction of various visual disorders. However, soft contact lenses which were developed and have been fitted since 1971, and which now have approximately 90% of the contact lens market, have been less than successful in the treatment of presbyopia. Presbyopia is characterized by loss of elasticity of the crystalline lens, and hence, loss of the ability of the eye to adjust to clearly see objects which are close and also those which are more distant.
Three common methods for correcting presbyopia are the use of bifocal eyeglass lenses, bifocal contact lenses, and monovision contact lens fitting. (One eye has a distance lens, the other is fitted for near-vision). Eyeglass lenses generally have two portions ground for two viewing distances. Since the eye will move in relation to the eyeglass lens, the patient can easily view through either lens; by gazing straight ahead for distance viewing, or looking down for near viewing.
Another method utilizes bifocal contact lenses. One type of bifocal contact lens is quite similar to eyeglasses in that it moves relative to the eye in order to place the correct portion of the lens over the pupil for viewing. These contact lenses have a lower segment for reading, which is engaged by the lower lid when the patient looks down and the eye rotates downwardly, causing the lens to move upwards on the cornea onto the visual axis for near viewing. These lower segments can be either lathed, fused, or molded and these lenses have a base-down prism in them to orient the lens on the cornea so that the reading segment is on the lower part of the cornea when looking straight ahead for distance viewing.
To eliminate the ned for the base-down prism, other types of bifocal contact lenses have been developed -- such as the concentric and aspheric designs.
In 1961, Morris Green, M.D., Pacific Contact Laboratories, Los Angeles, Calif., in an ad in the Mar. 15, 1961, copy of The Optical Journal and Review of Optometry described a hard bifocal contact lens with a bifocal in the upper part of the lens, that decentered down with blinking. The dynamics of the eyelid on hard contact lenses are much different than for soft contact lenses, since the hard contact lens sits on a coat of tears on the cornea and rests only slightly under the upper lid and near the lower lid edge. Thus, it does not conform to the cornea, limbus, and sclera as a soft contact lens does. Furthermore, the soft contact lens area is approximately 2 to 3 times larger and fits largely under both lids.
Present day hard (or rigid) bifocal contact lenses are designed with the bifocal in the lower portion of the lens with a base down prism for orientation. Such contact lenses have a thick lower edge that engages the lower lid and moves the lens up in downward gaze for clear near vision. These lenses are up to 90% successful.
Soft contact lenses were introduced in the early 1970's. Present day soft bifocal contact lenses designed with a lower bifocal segment and base down prism are not effective because the size of the lens puts the lower edge under the lower eye lid, making it very difficult to move the lens up. It is therefore a general object of the present invention to provide an improved soft multi-focal lens by increasing the amount and direction of movement of the reading portion to move over the pupil and into the visual axis by moving in a downward direction, and also increasing the "near vision" function of the lens.
Another object of the present invention is to provide an improved soft multi-focal contact lens.
Yet another object is to provide a soft multi-focal contact lens which is economical to manufacture, and more successfully fit by the practitioner.
These and other objects will be apparent to those skilled in the art.